Does anyone have an objection to the complete removal of the plain
filters (PLAINHTML and PLAINFOOTNOTES)?
These are all kinds of bad. They essentially serve to style plaintext
modules and toggle footnotes in plaintext modules, and they achieve this
by making big assumptions that are unlikely to be correct today (though
they might have been in 1999, when these were written).
For example, if you find {curly braces} in a plaintext module in 2013,
it's unlikely to represent footnotes. We long ago move all such
pseudo-markup systems to real markup formats.
The one useful feature (maybe?) is that <, >, and & are escaped by the
PLAINHTML filter. But I'm fairly certain no one actually uses this
filter in any front end, so even that is of no use in 2013.
--Chris